Utilisation of fly ash and sewage sludge ash based geopolymer with cement for the production of compressed stabilized earthen block

In light of the global housing crisis, Compressed Stabilised Earth Blocks (CSEBs) offer a sustainable and cost-effective alternative to conventional construction materials. However, traditional stabilisers such as cement and lime contribute to environmental degradation through high carbon emissions and resource depletion. This study explores the use of industrial byproducts, namely fly ash (FA) and sewage sludge ash (SSA), as alternative geopolymer precursors for CSEB stabilisation. Three methods were examined: geopolymer only, cement only, and a hybrid approach, using ash contents from 0 to 30% and cement dosages of 0%, 5%, and 7%, with a fixed FA to SSA ratio of 3 to 2. After 28 days of ambient curing, hybrid samples with 20%-25% ash and 7% cement achieved unconfined compressive strength up to 11.36 MPa, split tensile strength of 1.49 MPa, and flexural strength of 2.81 MPa. Water absorption ranged from 11.78% to 21.3%, indicating enhanced durability. Submersion and efflorescence tests confirmed stability under moisture exposure. Microstructural and chemical analyses using FESEM, EDX, FTIR, and DSC-TGA validated the formation of sodium aluminosilicate hydrate (N-A-S-H) and calcium aluminosilicate hydrate (C-A-S-H) gels. The integration of geopolymer and cement enhanced both mechanical and durability performance while promoting environmental sustainability.